Scott, best of luck with the DWC system.
Here are some suggestions:
You may want to switch it to a RDWC (Recirculating)...if you have the room. It's an extra bucket, but you'll love the simplicity. I had a DWC system and then built it to a recirculating system. It definitely helps to keep the temps lower. Temperature change in one bucket fluctuates a lot more than water in 5 buckets. With the extra bucket, you could add your ice packs and not worry about anything touching your roots.
Your weed plants love room temperature. So if your tent/room is running a little hot, increase your circulation. Cool down your room and you'll cool down those pails. The moment I switched my lights to the new LED Samsung diodes, it decreased my heat tremendously.
Another thing you could do is switch your lights so they come on during cooler temps in your house. (like at night) and have the lights off during the day when it's warmer out. Of course this depends where you live and what your set-up is like. I have a basement, so i keep my pails on the cement basement floor, which helps regulate the water temps.
Here's your best idea, place a reflective or mylar film across the top of your pails, having the plant come out the middle. So the light is blocked from your medium. I'm assuming your using some form of clay pellets as your medium? And...the baskets that you use to hold the media, it comes in different sizes, 10" and 6". The smaller ones keep the light out more but the bigger ones provide a larger root base.
Just thought i'd give you some ideas other than buying a water chiller.
SwitchH2O
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4’x4’x8’ frame built grow room
Spider Farmer SE3000
4†Vivosun powered intake
8†Vivosun outtake with 8†Filter
RDWC (Recirculating Deep Water Culture System)
Rockwool starter with clay pellet medium
Combination of Remo, Advanced Nutrients and a proprietary blend.
2nd last grow - 19.98% THC
Last grow - 22.23% THC
CURRENTLY GROWING
White Tahoe Cookies - 3rd week of flowering